Color management for color inkjet printers
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The purpose of a color inkjet printer is to print a high quality image of a computer generated color image or color image from a scanner. The color management of inkjet printers mainly includes: color matching between input devices; matching between original color and display color; color matching between output devices; matching between display color and print color; color between original and printed matter match. Color management is to solve the problem of color conversion matching between various devices. Because of the many influencing factors, printers can be said to be the most difficult part of the color management system. The way a color is represented by a printer is quite different from how it is represented on an input device such as a display. This is a subtractive method. The three primary colors are C, M, and Y, which are represented by toner and ink droplets.
There are two ways to introduce the color management system of the printer. One is bundled with professional color management software. The color management is completely done by the software. The printer only makes simple output. The other way is that the printer itself integrates color. Management system, color management is done by the printer. Either way, it is to output the exact color, which is what people often say needs to print the same color as the printed color or the color seen on the screen. This process is the ultimate goal of color management - "what you see is what you get".
So how do you manage the color of your printer? Mainly from three aspects of equipment calibration, production equipment color characteristics file, color conversion.
First, equipment calibration
Equipment calibration refers to calibrating the equipment to the standard so that the equipment achieves the best color expression. Equipment calibration is a prerequisite for color management. If the state of the device itself is not good, it will affect the latter part of color management. The input device mainly refers to the display. The purpose of display calibration is to calibrate the color balance of the input device, the contrast, and the color balance of the three primary colors of RGB. The output device mainly refers to the printer. The printer is color-calibrated according to the device parameters provided by the printer manufacturer, so that the printer outputs according to the factory output characteristics.
A Lab color space B display color space C printer color space
In the figure, A indicates the color space that can be seen by the human eye, and the color space of the display B display. The specific color range can be determined by its physical characteristics and the corresponding color profile. The display is tuned to give the display an optimal brightness, contrast, midtone, color balance and white field color. That is, the color cast of the display is corrected with the appropriate brightness and contrast so that the gray color of the display remains neutral gray. The image displayed on the screen can be made close to the print of the image. Printer color space: Corresponds to the black frame portion of the printer in Figure C. The specific color range that can be represented is determined by its physical characteristics and the corresponding color profile.
Second, ICC Profile
The device characterization file allows you to use the color conversion program to map between the device's color space and the CIE Lab color space. The working process of the color characterization file is to convert any input color information into a color in the CIE color space. In turn, it can convert the color of the CIE color space into the color reproduction space of the output device. We use the standard ICC color characterization file format, which serves as a standard for describing the color reproduction capabilities of devices from different vendors.
The ICC file base of the printer used by different color management software is different, so the printer ICC file between softwares cannot be used universally. For example, COLOR PROOF and SCREEN PROOF software need to adjust the basic linearity of the printer before controlling the ICC Profile, control the ink output of the printer, and then combine the data measured by the spectrophotometer with the basic linearity of the printer to generate a printer. The ICC file (ie Paper Profile); the Color Tune software's printer ICC file is generated by combining the printer density curve. The establishment of printer ICC files is closely related to printer ink droplet combination, ink output, resolution and other printing parameters. Different ink output and resolution require different printer ICC files.
Although the printer's ICC Profile should be fixed if the printing device, media, and ink type are fixed. However, due to the difference between the same type of printing equipment, media and ink, such as: the same type of inkjet printer, the working state of the printer heads of different printers is not the same, the amount of inkjet is not the same, so that the output is Imaging characteristics are also different. Therefore, this requires digital proofing color management software to achieve a certain standard by correcting the ink output (print density) of the printer to achieve the versatility of the ICC profile of the printer's own characteristics. When the working conditions of the digital proofing system change, it is only necessary to re-calibrate the ink output (print density) of the printer to ensure the color stability of the entire proofing system.
Third, the color conversion method
Color conversion is a bridge between color image data and device-independent color space. In short, regardless of the mode color conversion used, the color output from the display and color printer must be as close as possible to the scanned original. Color Conversion: The software driver first converts the RGB representation of the computer into a CMY representation used by the printer. This conversion process determines the relative amount of each primary ink used when printing the desired color. The software driver first converts the RGB representation of the computer to the CMY representation used by the printer. This conversion process determines the relative amount of each primary ink used when printing the desired color. Halftoning Subsequently, the software driver uses a process called halftone to convert the CMY representation into a series of color printhead nozzle on/off commands (each with a set of nozzles), which is also monochrome (usually It is black) The print head nozzle prints text and images to produce a series of on/off commands. The CMM Color Management Module generates a signal value of appropriate size by the device driver based on the device profile. If the color device is properly characterized, then the CMM should produce the effect that the user wants. For example, with a profile file for the monitor and printer, the same image printed by the monitor and printed by the printer should be very similar.
Fourth, the impact of print media
The first is to choose whether the quality of the inkjet paper used is good, as well as the cleaning status of the nozzle, the vertical and horizontal calibration, the balance of the gray scale and the resolution. After these pre-questions are completed, it is necessary to calibrate each tone, and each level should be clearly defined. For example, the printer prints a four-color guide to measure with a spectrometer, and then calculates and then corrects This is a special feature of RIP; however, if you want to print directly, there is no way to do calibration (Calibration) or Base Nearization without RIP. To measure the color space printed on the paper by the printer, and then read the color through the instrument. Although different instruments have different guides, the number of patches will be different due to the different distribution of the instruments, but The final result is the same. The device profile defines the gamut space of the printer, such as the print guide (TC918 RGB, 918 patches).
The quality of the print media also directly affects the production of printer profile files, which can also interfere with the color management of the printer. Good media should have a smooth surface, good chargeability, proper whiteness and high resolution. If the surface of the media is not smooth enough, it will consume more toner, and a smooth surface will reduce the consumption of toner. Good media also have excellent performance in moisture content control (up to 5%), high moisture surface resistance, low moisture and high surface resistance. The printing process of a color laser printer is done by the movement of electric charge, and the image printed on the low-resistance medium generates noise and affects the output quality. When you create a device profile, you must select the media you want to use as a print reference.
Points to note in display design: Display device eigenvalues such as brightness and contrast must be recognized and processed by the operating system for proper color management. Points to note in printer design: The printer should be prepared to communicate with the user to adjust color. The internal monitoring capability should be able to monitor the density and spectral data of the printed colors. The printer should be able to understand the characteristics of the paper and ink to some extent for use by the operating system and advanced color management software to control the output of the printer. Through the above adjustments to the printer and display, the goal of color management can be achieved in print: WYSIWYG.